For electrically processing an image related data, the data is encoded to generate a code to be recognized by a machine, such as a computer. For transmitting an image data via telephone line, radio waves, or the like, the image data is generally compressed to reduce the amount of data to be transmitted.
There has been proposed an image data encoding apparatus which uses the adaptive arithmetic encoding technique. In arithmetic encoding, a probability real-number line is divided into two intervals at a rate corresponding to the probability (1 or 0) of a symbol sequence to be encoded The binary decimal value indicating a boundary point (lower bound) of the divided interval becomes an output code of the apparatus. An arithmetic encoding technique according to "ISO/IEC 1544" is applied especially to a transmission/receiving system, which processes a binary (bi-level) image to be processed by an apparatus such as a facsimile machine.
According to conventional apparatuses, there is a disadvantage in that a normalization (re-normalization) process can not be performed in a stable period of time; and therefore, it becomes difficult to realize a real-time encoding porcess.
For solving such a problem, an encoding apparatus has been proposed in Japanese Laying Open Kokai No. H6-121172, which includes a monitor means for monitoring the contents of an interval register (A-register), and a shifter means for shifting the data in the interval register a plurality bits at one time, in accordance with the monitored information. With this kind of apparatus, the normalization (re-normalization) process can be performed in one clock cycle (stable period of time), however another problems arise. Namely, it is difficult to improve process speed. In addition, it becomes difficult to realize a real-time encoding process if a symbol (image data) to be encoded is inputted for every clock cycle.